HHdev Force 2fa email for all users. Use as mu-plugin. Needs the https://wordpress.org/plugins/two-factor/ plugin to be active.

hhdev-2fa-set-email-2fa-all-users.php

<?php
/**
 * Plugin Name: HHdev Force 2fa email for all users
 * Version:     1.0.1
 * Description: Needs 2FA plugin to work. Forces alle users to 2fa with email.
 * Plugin URI:  https://haha.nl/wordpress-plug-in-op-maat/
 */

/*
There is also an open issue for enabling 2FA for all users which includes a temporary solution for doing that through a filter:
*/

// set the 2fa forced.

add_filter(
    'two_factor_enabled_providers_for_user',
    function( $providers ) {
        if ( empty( $providers ) && class_exists( 'Two_Factor_Email' ) ) {
            $providers[] = 'Two_Factor_Email';
        }

        return $providers;
    }
);